There seems to be some sort of forgone conclusion that you should stop applications of N as fall approaches. You'll find mostly anecdotal evidence suggesting this as appropriate, but little, if any, scientific. In some circles convention dictates we only fertilize while plants are in actively growing, or from bud break - late summer. I often see it contended that late (fall) feeding of N is sure to 'force' new growth and the new growth will be killed by frost.

But first, all tender new growth is killed by frost. Second, and probably more importantly, please consider that bud set occurs in mid-late summer, and while it takes N to fuel new growth, N plays no role in the initiation of bud-break. For that stimulus, look solely to photo-period. No one turns off the N supply where trees occur naturally - yes?

The acquisition of resistance to chill is related to both photo-period and decreasing temperatures and is actually improved with regular balanced N supplementation, so there is no reason not to continue supplementing N through fall and into early winter. Let your guide be soil temperatures. As long as soil temps are >55* plants will assimilate and store not only P & K, but N as well. This (tendency to store N) plays a pivotal role in fueling new growth in spring when soil temperatures are reduced and assimilation of N is depressed. BTW - please do not fertilize with organic sources of N like various meals, fish/seaweed emulsions, or urea when soils are cooler than 55* (ammonium toxicity).

Al

Because nitrogen is so often deficient in an actively growing landscape, the addition of ammonium nitrate
usually restores shoot growth. Phosphate addition, on the other hand, often has no apparent effect
(probably because it's generally not limiting in perennial landscapes. This observation has led
landscapers and fertilizer manufacturers to claim that phosphorus stimulates root growth (there is no shoot
growth, ergo it must be stimulating root growth). The unfortunate result of these assumptions is the
mantra "nitrogen for shoots and phosphorus for roots." While there are no nitrogen toxicity symptoms
per se, the same cannot be said for phosphate toxicity.
The result of phosphate overfertilizing is leaf chlorosis. Phosphorus is known to compete with iron and
manganese uptake by roots, and deficiencies of these two metal micronutrients causes interveinal
yellowing. It's my belief that many of the chlorotic shrubs we see in urban landscapes are suffering
indirect iron (or manganese) deficiency from overapplication of phosphorus. Moreover, it has been
experimentally demonstrated that high levels of phosphorus are detrimental to mycorrhizal health and
lower the rate of mycorrhizal infection of root systems. This mutually beneficial relationship between the
fungus and the plant roots allows the plant to more effectively explore the soil environment and extract
needed nutrients. In the absence of mycorrhizae, the plant must expend more energy growing additional
roots and root hairs to accomplish the same task

Here is a link that might be useful: The Myth of Phosphate Fertilizer

The point is .....?

I think the link I left to something I wrote about high-P fertilizers pretty closely parallels Dr. Scott's thinking.

Al

Here is a link that might be useful: More about high-P fertilizers from Al's view

Both good articles and should be read, and most importantly, understood by any serious gardener.
Years ago I used to fertilize my maples with lawn starter fertilizer. I had so much new growth the aphids moved in. Eventually the predators got em', but in the meantime they did so much damage to the maples, they looked like heck. I don't use any fertilizer on my in ground plants anymore, just wood chips. No significant aphid problems now.

I make my own potting soil using aged woodchips, sand, and a little good loam. I rarely keep a plant for more than one season in the same pot. Almost all are eventually planted out. With ten acres, I have a lot of room. It's running out though, after more than thirty years here.

I'm not growing for commercial production, so I don't need to keep the tolerances as close as some might.

Mike

{{gwi:1049515}}